The invention relates to an operating apparatus having a manually operable touch-sensitive surface with an associated actuator system for providing a haptic feedback signal on the basis of a touch.
Such operating apparatuses having a touch-sensitive surface are used in many different ways in the form of what are known as touchscreens or touchpads. They can be used wherever the surface is intended to be used to input control commands and the like, for example on control panels or monitors, but also on portable equipment such as mobile telephones, tablet PCs, laptops and the like.
Such operating apparatuses are a combined input and output appliance in which the operation or program execution of an appliance, as indicated above, can be controlled directly by touching particular surface regions defined by a displayed image. In this case, control is usually effected using the finger, but it is also possible for it to be carried out using a stylus.
Usually, a touch-sensitive surface of this kind or a touchscreen of this kind comprises three elements. Firstly, the touch sensor, in addition an associated controller and also a software driver. Downstream of the touch sensor there may be a screen on which the image defining the sensitive input regions is displayed, said image being visible through the two-dimensional touch sensor, that is to say the actual touch-sensitive surface. The touch sensor itself usually has a touch-sensitive layer, comprising optical glass or a flexible polyester layer. In order to sense a signal-generating touch, a current usually flows through or via this surface, and this, in the event of touch with the finger or the like, brings about a voltage change or a signal swing that is sensed and evaluated in order to ascertain the touched position and hence in order to capture an input command. The controller is used to sense such user inputs on the touch sensor, that is to say ultimately the touch-sensitive surface, and to forward them as signals, which signals are processed by the software that is installed on the appliance in order to interpret the touch-related signals delivered by the controller.
The design of the touchscreen or touchpad, that is to say the touch-sensitive surface itself, may differ depending on the underlying technology. By way of example, resistive touch surfaces are known, comprising an outer plastic film layer and an inner glass or plastic pane, which are separated by spacers. The areas associated with one another are coated with an indium tin oxide layer (ITO layer). ITO is a translucent semiconductor. A low test voltage that is used for actuation is applied to one or both ITO layers. When the outside layer is now pushed locally, the result is local electrical contact between the ITO layers, and an electrical resistance is produced, the effect of which on the voltage ratio of the voltage tapped off allows ascertainment of the touch point relative to the respective margin of the layer. The basic design of a resistive touchscreen of this kind is known.
A further basic design is that of a capacitive touch surface. This comprises a glass substrate coated with a transparent metal oxide, usually again an ITO layer. The corners of the sensor are provided with electrodes to which a test or operating voltage is applied that is used to produce a uniform electrical field. The surface is statically charged by the latter. A touch with a capacitive medium, which is what a finger is, triggers charge transfer. Capacitively bound charge transfers to the finger, and there is a flow of current that is measured at the corners of the touchscreen. There is therefore a disturbance in the electrical field, and the flow of current is in direct proportion to the position of the touch. The associated controller again senses the relevant signals, and the software evaluates them.
A third basic design that is known is also optical touch surfaces. These comprise a matrix comprising light-emitting diodes and photodetectors. The light-emitting diodes shine on the detectors on the opposite side. A touch on the surface interrupts the beam of light and hence caters for a measurable signal drop that can readily be resolved locally. That is to say that the controller locates the touch point. This basic touchscreen design is also sufficiently well known.
In addition, touch surfaces are known that provide the user with a haptic (tactile) feedback signal when he has successfully made a signal input and he releases the pressure on the surface. This haptic or tactile feedback signal serves to perceptively signal the successful signal or command input to the user. To this end, a suitable actuator system is provided. Inertial actuators are known for this, usually comprising a motor that turns an eccentrically mounted mass, or comprising a spring/mass system that is capable of oscillation.
Alternatively, piezoelectric actuators are known, which can be produced in a very thin design with a very fast reaction time. The use of a piezoelectric actuator of this kind, which may also be of pane-like design, for example, involves the touch surface either being bent or being pushed against another area, so that a displacement movement is produced.
Such an actuator system can thus be used to set the touchscreen or the touchpad, that is to say the touch-sensitive surface, in motion such that there is a haptically perceived “click” for the user upon the exertion of pressure on the surface. It is then possible both for pushing the surface and for releasing the pressure on the surface each to produce a separate actuator-like movement. To emulate the mechanical click as realistically as possible in this case, it is necessary to allow the actuator system to be triggered as promptly as possible. Whereas the “push” click can be recognized in relatively delay-free fashion by compressive force sensors situated under the touchscreen or touchpad, the “release” click, that is to say the removal of the finger from the surface, can involve delays on account of the sluggish system mass, as a result of which an imprecise click sensation is produced.